Biotic and Abiotic Factors
Freshwater is filled with both Abiotic factors and Biotic factors. Abiotic factors can include rocks, the water itself, sand, trash, and air currents. These are all Abiotic factors because they are not living organisms. Biotic factors in Freshwater would include fishes, grasses, crayfish, clams, and mosses. These are Biotic factors because they are living organisms. If any one of these factors, Abiotic or Biotic, were to disappear, other factors in this ecosystem would change as well. For example, if the rock were disappear, the crayfish would have nowhere to hide from fish, and then fish would flourish in that body of water.
Density Factors
In Freshwater, density dependent factors could be disease and parasitism. Although there are many more, these are common factors found in fish and other aquatic creatures. A density dependent factor would be a problem that depends on a large population to proliferate. There are also density independent factors, which can include weather and natural disasters. These are density independent factors because they do not require a large population to cause damage.
Organisms
Producers and consumers are opposites of each other; one makes food, producers, and the other consumes other organisms or their wastes, consumers. Producers are usually plants, but can be certain types of bacteria as well. The most common producers at Freshwater are mainly grasses and trees. For example river birches, willow trees, water stargrass, water lilies, duckweed, cattails, reeds, and tapegrass all grow by water. Two bacterial producers that can be found in Freshwater are algae and plankton. Consumers are the other types of organisms; animals, fungi, and the bacteria that does not make it's own food. Animals make up the majority of consumers in Freshwater. Consumers can be many things, including ducks, geese, platypi, snakes, crocodiles, alligators spiders, insects, and salamanders. It does make sense that animals have the majority, having over 1,000,000 species, but in Yellowstone National park, there are places where large quantities of bacterial consumers can be found. Archeabacteria live in the very hot springs that can be found in the park.
Endangered Species
The Mekong Catfish is a critically endangered species. Growing up to weigh 150-200 kg in six years, this fish is one of the largest Freshwater fish to date. It's picture can be seen in the upper right corner, and one can see that it is of monstrous proportions. It's scientific name is Pangasianodon gigas. This fish is becoming extinct because of over-fishing and the decrease of water quality due to development and damming upstream. The channel of water that these fish live in is the Mekong River, which is where their name is derived. Experts believe there may only be about a hundred left in the world.
There is also the Amazonian Manatee, Trichechus inunguis, that is not so badly endangered, but listed as vulnerable. The animal is endangered because of hunting, calf mortality, climate change, and habitat loss. It also gets it's name from the river it lives in, the Amazon. It can not be properly counted because of the murky water it lives in.
American Crocodile, or Crocodylus acutus, is also a vulnerable freshwater animal. In the 1970s there were only a few hundred left, but now the numbers are up to about 2,000. The organism is endangered because of hide hunting, pollution, loss of habitat, and removal of adults for commercial farming. This organism also can live in Saltwater, but is more commonly found in freshwater.
There is also the Amazonian Manatee, Trichechus inunguis, that is not so badly endangered, but listed as vulnerable. The animal is endangered because of hunting, calf mortality, climate change, and habitat loss. It also gets it's name from the river it lives in, the Amazon. It can not be properly counted because of the murky water it lives in.
American Crocodile, or Crocodylus acutus, is also a vulnerable freshwater animal. In the 1970s there were only a few hundred left, but now the numbers are up to about 2,000. The organism is endangered because of hide hunting, pollution, loss of habitat, and removal of adults for commercial farming. This organism also can live in Saltwater, but is more commonly found in freshwater.
Keystone Species
A keystone species in freshwater could be plankton. This is because they are the basis of the ecosystem, providing for the primary consumers and so on. If not for these tiny producers, the entire ecosystem would fall apart. That's why a keystone species would be freshwater plankton.
Predation
Predatory relationships are when organisms eat other, lesser, organisms. In Freshwater, there are many predatory relationships. As with Anacondas, and the Capybara, or Crocodiles and Wild Boars, or maybe even Piranha and Cows, there are predators to be found everywhere. Anacondas are found in South American countries, along with Capybara, the largest rodent in the world. The large snake is known for eating large animals with its vice-like grip; and the Capybara is a good size for swallowing whole. Crocodiles will also eat larger animals and are known for their ferociousness when hunting. The Wild Boar is a formidable opponent, but not a match for the jaw strength of the Crocodile. The Piranha, an almost iconic creature, is not what most people think them to be. Although a certain type of Piranha, the Red Belly, is capable of the fabled dilaceration of cattle, most do not hunt this way. Still, all Piranha should be feared, because they are cunning hunters and very good at killing.